Using a neodymium magnet ($6 from Amazon), I checked my ancient bronze coins. Several could be picked up onto the magnet, and many more reacted slightly. The coins that the magnet picked up include Lydia/Sardis, Thrace/Rhoemetalkes, Caracalla, Philip, Constantine, Constantius II, Jovian, Valens, and a tiny late Roman (Arcadius-ish). And an obvious fourree of Caracalla. Also several from the junk box. Apparently, magnetism in ancient bronzes is not a sign of a fake coin (except for fourrées with iron or cobalt in their cores), but rather occurs because bronze coins could contain a range of metals. A Coin Talk search for “magnetic” shows references to magnetic coins scattered in threads about individual coins. In one thread, Mike Margolis linked to a thorough discussion in ForumAncientCoins, which states: “I did find it interesting at first just to realize some of the bronzes were 'magnetic' at all. … It wasn't so much a matter of being 'pure' or 'impure', rather the specific metals making up the bronze alloy and their proportions. The ranges of alloys in ancient bronze coins is highly variable to begin with. The presence of enough iron and cobalt to make a bronze 'magnetic' is fairly unusual, but those coins aren't necessarily more 'impure' than others with lead or other peculiar alloy components.” PtolemAE “Cobalt and iron are closely associated with copper ore deposits and can be quite difficult to completely separate out during the refining process. … Additionally these trace elements might help determine the location on the copper deposits used in this coinage. Do the coins with magnetic properties come from the same region?” Cameron http://www.forumancientcoins.com/board/index.php?topic=49787.25 Any other info that might be appreciated by people searching Coin Talk for information on magnetic ancient bronzes?
Interesting topic, checked my Roman Republic AE collection,non are magnetic, same for my roman Sestertii collection. Didn't check my Late Roman bronze , these are all in holders, but if someone is interested I can do that. Have one Dupondius of Domitian wich is medium strong magnetic: Gordian III provincial , medium strong magnetic: and 2 coins from Sicily ,which are strong magnetic:
http://www.forumancientcoins.com/dougsmith/quest.html I asked this question on a page in 1997 and never went further with the matter. I have not checked the coins obtained since that date. Geta AE18 Pautalia / Aesculapius, ex. Tom Mallon
